The invention relates to an optical disc player and to a method of detecting different types of optical disc inserted into the player.
Various types of optical discs are known which have been developed according to different standards for the recording and/or replay of data. This data may represent audio or video signals or may be pure data. High reflectivity discs, which may typically be CD Audio, CDROM, DVD, or CD recordable, often referred to as write once read many (WORM), generally produce a reflected signal which is of relatively large amplitude. Re-recordable discs, which may typically be CD-RW or CDRAM, however, generally have a lower reflectivity and consequently the reflected signal will have a lower amplitude. As a result, in order to optimise the decoding of the data on the discs it is desirable to provide different parameters for the detection circuits within the player for the different types of disc.
Generally optical disc players are set to focus on a high reflectivity disc and if focus is not found, that is the reflected signal does not reach a preset threshold level, then the player parameters are changed on the assumption that a low reflectivity disc is present. An attempt is then made to focus using parameters appropriate to a low reflectivity disc. If focus is still not found an indication is given that no playable disc is present. This procedure has been published in EP-A-0789354 and is satisfactory provided that the player does not focus on a low reflectivity disc when using parameters appropriate for high reflectivity discs. Initial focussing is generally attempted when the disc is stationary in the player. It has been discovered that under these comparatively ideal conditions some nominally low reflectivity discs may allow focus to be achieved since the detected reflected signal may marginally exceed the threshold value set. When, however, the disc is rotated there is then insufficient noise margin to allow the data to be reliably read from the disc particularly when jumps from one radial position to another are performed. In addition the rotation of the disc is controlled by a digital phase locked loop (DPLL) working on the data read from the disc and if the data is not read correctly the DPLL may lose phase or frequency lock resulting in the spinning out of control.
In this specification non-recordable discs include high reflectivity WORM type discs in addition to those which are preformed and unable to record any data.
It is an object of the invention to enable the provision of an optical disc player that is able to discriminate more reliably between different types of disc so that it can more reliably read data from different types of disc.
The invention provides a method of detecting the type of optical disc inserted in an optical disc player comprising the steps of;
i) attempting to focus a laser read head on the disc using a first set of player parameters appropriate for a first type of disc,
ii) if focus is obtained
a) reading data from the disc and determining whether a sub-code representative of a second type of disc is present,
b) if so changing the first set of player parameters to a second set of player parameters appropriate to a second type of disc,
c) if not playing or indicating the presence of the first type of disc,
iii) if focus is not obtained changing the first set of player parameters to said second set of player parameters,
iv) if focus is then found playing or indicating the presence of the second type of disc.
By attempting to read data which is only present on re-recordable discs, hereinafter referred to as read-write discs it can be ensured that read-write discs are read using player parameters appropriate to lower reflectivity discs regardless of whether the player was able to initially focus on the disc using the parameters appropriate for high reflectivity non-recordable discs. This has the advantage that read-write discs of comparatively high reflectivity, but not as high as non-recordable discs, can be reliably identified and the player optimised for their playback rather than attempting to use the wrong set of parameters merely because focus was originally found. An alternative solution would have been to increase the threshold required for obtaining focussing of high reflectivity non-recordable discs but this would have the disadvantage of possible failure to focus on lower reflectivity non-recordable discs.
Step ii) a) may be performed by reading a table of contents and determining whether mode 5 sub-code is present in the Q sub-code channel. Read-write discs conforming with part 3 of the Orange Book Standard contain a mode 5 sub-code and in this way relatively high reflectivity read-write discs on which the player may be able to focus when the disc is stationary but where it may lose focus when the disc is spinning or when the read head jumps from one position to another across a plurality of tracks can be identified. The appropriate measures can then be taken to alter the player parameters to more reliably maintain focus and read the data
The method may further comprise when focus is found in step iv) the steps of;
vi) reading data from the disc, and
vii) determining whether mode 5 sub-code is present before indicating the presence of the second type of disc.
In this way it can be ensured that it is a recordable disc being played rather than a low reflectivity non-recordable disc.
If focus is not found in step iv) then the method may further comprise the step of;
v) indicating that no playable disc is present.
The player parameters may comprise the gain of an amplifier forming part of a data tracking loop and/or a sensitivity control for processing individual diode outputs from the read head.
The invention further provides an optical disc player capable of detecting the type of disc loaded in the player comprising means for setting a first set of player parameters appropriate for playing discs of a first type, means for focussing the read head on the disc, means for reading data from the disc, means for processing the data and detecting the presence of a sub-code representative of a second type of disc, means for setting a second set of player parameters appropriate for playing a disc of a second type if the sub-code is present, and means for setting the second set of parameters if focus is not found using said first set of parameters.
The optical disc player may further comprise means for indicating that no readable disc is present if focus is not obtained using either the first or second set of parameters.
The sub code representative of the second type of disc may be a mode 5 sub-code in the Q sub-code channel. Such sub-codes are always present in CD-RW discs conforming with part 3 of the Orange Book Standard and serve as a means of detecting the presence of such discs regardless of whether their reflectivity is sufficiently high that the player can focus on them using parameters optimised for high reflectivity CD Audio or CDROM discs.
The gain of a high frequency amplifier which amplifies the sum of the diode outputs from the read head may be increased for low reflectivity read-write discs. Alternatively or in addition the sensitivity of an analogue to digital converter block to which individual diode outputs are applied may be increased for low reflectivity recordable discs.